Sunday 1 June 2008 20.07 EDT
First published on Sunday 1 June 2008 20.07 EDT

Yves Saint Laurent, who has died at the age of 71, had a reputation as an artist, transcending fashion, which was encouraged by his entourage and endorsed by the French establishment.

However, his true importance was that he was the last of the Paris couturiers in the tradition beginning with Charles Worth in the 19th century and the first designer to invest his talent in what became the 21st century global market for mass luxury.

He was born in Oran on August 1 1936, when Algiers was still a department of France, the son of a businessman who also managed a chain of cinemas.

The boy began advising the family's chic women on how to dress, cutting miniature garments from his mother's old clothes and staging plays, which he also designed.

When he was 17, his father arranged for his sketches to be shown to the editor in chief of French Vogue and enrolled him at the official couture academy in Paris.

Boredom drove him out in months, although he won first prize in a major competition and presented Vogue with artwork that predicted Christian Dior's next collection. Dior took the ambitious youngster on as an apprentice in 1955, promoting him to assistant in 1957.

Dior anointed Saint Laurent as his dauphin, but nobody expected that any royal succession was imminent because Dior, after his New Look triumph in 1947, meant to mature slowly along with his clientele, in the Worth manner.

But Dior died suddenly, of a heart attack, at the age of 52. The textile magnate, Marcel Boussac, who financed the house of Dior, named three female staff plus Saint Laurent, the "crazy enfant", to take over.

Saint Laurent rushed back home and scribbled 1,000 designs in a fortnight. They were later edited by the three female staff, who chose the trapeze look as silhouette for his first collection in January 1958. The collection was a success.

Saint Laurent might not have survived alone but, within weeks of his debut, he met his spiritual spouse, his lifelong protector and promoter, Pierre Bergé, of whom he said: "His strength meant I could rest on him when I was out of breath." (Saint Laurent's repeated diva bursts of weakness micro-controlled the others in his life).

Bergé backed Saint Laurent in his Beat collection of 1960, which so alarmed the customers and Boussac that the house of Dior refused to contest Saint Laurent's army conscription later that year.

He was meant to fight in the Algerian colonial war, but collapsed during induction and was sent to a military mental hospital briefly before total discharge.

No job awaited - Marc Bohan had replaced him at Dior - but Bergé sued Dior for breach of contract, and with the damages, plus finance from a wealthy American, set Saint Laurent up in his own house (at first only a garret) with just enough cash for a single collection in 1962.

The critics may not have wept for joy, but customers bought the clothes, which soon boasted the sloping, loping YSL logo by the graphic designer Cassandre.

Through the 1960s, Saint Laurent did modern - safari and sailor jackets , the female tux with cummerbund he called "le smoking", short shifts inspired by Mondrian and Andy Warhol, trad craft with pop pizzazz - for the bourgeoise.

There was no going home after 1962: his family had fled Algeria for France, and all that he remembered was dismantled.

Instead, he found an unconflicted North Africa among the rich hippies of Marrakech in Morocco. He adopted fresh muses, or they adopted him - Betty Catroux and Loulou de la Falaise, two wild women who looked, like himself, feminised.

He lurked in Marrakech during the Paris anarchy of May 1968, returning with the sketches (and Bergé with the spin) for a collection that, although modelled in the old, staid mannequin manner, was described as the "first post-couture".

The real fashion revolution, though, was less in the line than in the licensing. Bergé had advised Saint Laurent to do ready to wear, and in 1967 the house opened a pret a porter boutique - Rive Gauche, Left Bank, named after the HQ of intellectual Paris.

Later, YSL supplied designs and the name, but the boutiques were franchised, while Bergé licensed the name to accessory manufacturers.

Perfumes, those attars of named glamour, had subsidised Paris couture houses since the early 1920s, and Saint Laurent followed his master, Dior, with Y in 1964 and Rive Gauche in 1968.

Around 1970, Saint Laurent, who had posed for Andy Warhol, understood that if couture did have a future, it was as loss leader for licensing deals promoting the sales of scent and mass-produced accessories.

The realisation coincided with his own introductory season of flamboyant behaviour.

How much drink and drugs he indulged in is uncertain (it was estimated he could get drunk on half a glass of wine and high on a puff of a joint), but he projected a personal, gay liberation when photographed nude by Jeanloup Sieff in 1971 as the image for his male cologne.

Saint Laurent's next creative experiments helped him cope with Bergé's exit from his private life and home (though not business); the latter was exhausted by 18 years of close proximity to his casebook of neuroses, and unhappy with his attraction to both substance abuse and a dangerous lover.

The estranged couple nevertheless spent $500,000 on a 1976 show that changed the way couture was presented.

They had a raised catwalk built and, as Alicia Drake wrote, the "tilt upwards of the audience's heads was enough to demonstrate the transformation of haute couture as wardrobe provider to haute couture as stage show".

The costumes from that Opera collection looked sublime in photographs, but were luxury brand enhancers rather than clothes. Saint Laurent's 1977 and 1978 shows were also magnificent pageants referencing exotic pasts (Spain, Morocco, China), and their primary purpose was to publicise the logo of his 1977 perfume, Opium.

After 1978, a museum tone dominated his designs. There were too many tribute collections, and the opulent ensembles were meant from the start to be exhibits.

By 1983, when he was 47 and celebrating the 25th anniversary of his debut, they were on retrospective display at the Metropolitan Museum of Art in New York, where they were seen by 1 million visitors.

The show went on the road around the globe and others followed, drafting in his perfected classics of the 1980s and such near-unwearable wonders as the 1988 jackets hand-beaded with Van Gogh paintings: visually and technically beautiful, yet not fashion - more like vestments.

Saint Laurent's physical health had been affected by depression, bouts of 150 cigarettes a day and drugs, both prescribed and recreational.

Yet through the 1990s he arrived at the grandest of galas to collect honours (Commander of the order of the Legion d'honneur, New York Fashion Council lifetime achievement award).

His brand stayed in the game, with ownership passing from Bergé/Saint Laurent to luxury goods groups: Sanofi to Francois Pinault to Gucci, which brought in Tom Ford to design YSL ready to wear in 1999, pastiching the great originals (the lean blacks, the imperial robes) but in the new, disposable mode.

Many claim Ford's appointment precipitated Saint Laurent's 2002 announcement of his retirement. "I feel I created the wardrobe of the contemporary woman," he said as he passed into internal exile in his apartment on the Rue de Babylone.

An archive of his work had already opened in La Villette, Paris, and in 2004, the couture house itself became the Pierre Bergé -Yves Saint Laurent Foundation, a shrine to his creative past.

Despite the separation of 1976, Saint Laurent and Bergé remained a devoted couple to the end. They bought and restored the Majorelle Gardens and the Villa Oasis in Marrakech in 1980.